Periodontal disease appears to be related to the overgrowh of certain anaerobic bacterial species in the periodontal pocket. Traditional treatment aims to mechanically debride these organisms from the tooth surfaces and to surgically remove the diseases gingiva. While this is a successful regimen, it is expensive and beyond the financial capability of many people. In this proposal we shall determine whether the usage of metronidazole, an antimicrobial whose spectrum of action is specific for anaerobes, can be integrated into a treatment regimen which is both effective and efficient compared to traditional treatment. We will compare traditional treatment to traditional treatment supplemented with short term metronidazole to determine the effect on the bacterial flora of the pockets, pocket recuction, and attachment gain during the hygienic phase, the actual need for surgery following hygienic phase treatment and the long term health and survival of the teeth in the mouth. Dental patients seen at the Universityh of Michigan School of Dentistry will be screened for the presence of advanced periodontal disease. Patients so identified will have the dental plaque from 3 to 4 diseases sites cultured and if high proportions of either spirochetes or Bacteroides asaccharolyticus are found, the patient will enter into a double blind clinical study involving the 7 to 10 day usage of metronidazole during the hygienic phase of therapy. All patients will receive the traditional treatment involving a hygienic phase, a surgical phase, and a maintenance phase, and will have their periodontal plaque cultured using quantitative anaerobic culuring procedures. The study will compare the clinical and bacteriological status of the two groups at each phase of treatment.